DE10221367B4 - Pneumatic centrifugal dryer - Google Patents

Abstract

A pneumatic transport rotor, recirculates a mixture of materials to be dried with vapors. In the course of recirculation, it causes the flow of falling material to be accelerated under centrifugal force, against the walls of the dryer. The heated walls act as a heat exchanger. An Independent claim is included for the corresponding dryer.

Description

The The invention relates to a method and an apparatus for drying pneumatically recoverable goods, in particular of wood fibers and similar vegetable Fabrics, in an indirectly heated spin dryer.

at the industrial drying of wood chips prepare the most establish the high efficiency applied to emission problems by thermal decomposition. Wood fibers become very industrial energy-intensive dried in stream dryers.

Tube bundle rotary dryer Previously considered as the dryer with the least amount of pollutants the drying of wood pulp. That's because these dryers gently heated indirectly with steam (or thermal oil). Of great disadvantage is the one for that required steam boilers, unless steam is available anyway Available. In normal tube bundles However, wood fibers get caught up. This is a special, expensive Heating register dryer of the company VETTER MASCHINENBAU GMBH KASSEL.

The EP 0 457 203 B1 claims a drum dryer with closed steam-air circuit, which is particularly suitable for the drying of substances with a strong odor, wherein the vapors are condensed and the non-condensable vapor fractions are burned. For this dryer, the use of the heat of condensation of the vapors is claimed. The patent also describes the heating of the non-condensable vapor fractions by means of flue gas coolers prior to their entry into the combustion chamber.

The EP 0 459 603 B1 claims method and system for drying wood chips, wood fibers or similar bulk materials in a Brüdenkreislauf in which the drier dryer leaving flue gas-free vapors are heated indirectly in a heat exchanger of the hot fuel gases and fed back to the dryer, with a partial flow diverted from this circuit and the thermal decomposition of the pollutants is conducted to the combustion chamber. A vapor condensation does not take place. The same procedure describes the EP 0 508 546 A1 ,

For the drying of substances in which a hard-to-clean vapor condensate is obtained, claimed the EP 0 714 006 B1 an improvement of the process of EP 0 459 603 B1 by heating the Brüdenteilstromes reaching for combustion with the hot, the combustion chamber directly leaving the flue gas, so that the following countercurrent heat exchanger for the extraction of the dryer heat at the hottest point is no longer so much thermally stressed. The residual heat of the flue gases is then still used to heat the combustion air and optionally still for a predrying.

As is well known, gases are poor heat carriers due to their low density, and evaporative condensation circuits transfer the heat best. The EP 0 851 194 A3 claims that the hot flue gas of a combustion chamber first heat is removed by a steam generator, before being heated in a second heat exchanger, the vapor cycle. The vapor excess is burned. Preferably, as a dryer obviously a tube bundle rotary dryer with housing or with rotatable drum is used, wherein a current dryer can be connected upstream. With this arrangement, lower exhaust gas temperatures should be achievable. It is not clear from the illustration whether this arrangement has economic advantages over the classic tube bundle rotary dryer with only one heat carrier circuit.

After DE 100 56 459 C1 can fibrous substances with low bulk density and high internal friction, such as wood fibers basically not in a dryer after the EP 0 714 006 B1 or the DE 196 54 043 C2 be dried. Therefore, a method is claimed for a dryer, which is obviously a stream dryer, with circulated between the dryer and the heat exchanger heat exchanger vapors and with vapor condensation, as it is already in you EP 0 365 851 B1 was claimed for a drum dryer, wherein the non-condensed vapor fractions are passed over a heat exchanger in the furnace, as in the EP 0 714 006 B1 for the disposal of vapors without prior condensation is claimed. In subclaim 9, the use of a current dryer for the method is then claimed.

The DEUTSCHE BUNDESSTIFTUNG UMWELT initiated the development of the The superheated steam dryer Company SCHENKMAMN & PIEL, LEVERKUSEN promoted. This is one with 0.5 to 1.5 bar overpressure operated 100 m long power dryer with little overheating the circulatory vapors (<180 ° C) to avoid gaseous Emissions. For 1 kg of water evaporation must About 50 kg (!) vapors are circulated in this dryer.

Most drying processes are unfavorable in terms of control engineering. The DE 196 06 472 C1 be writes, as in a continuous dryer already at start the target residual moisture can be achieved quickly by a complex control. The DE 196 09 530 A2 describes a two-stage drying of biomass, wherein the hot biomass of the first stage is set in a downstream flow dryer by controlled evaporative cooling with conditioned supply air to the exact processing moisture. The EP 1 128 145 A2 describes the control of a power dryer by recording the climate data within the dryer with pressure, temperature and humidity sensors whose signals are evaluated by a controller that regulates the temperature of the hot gas stream.

A problem with multi-stage dryers, for example the widespread combination current dryer for predrying and drum dryer for main drying, is the amount of the guided through the entire plant steam, its separation after the predrying the DE 44 27 709 A1 describes.

With Indirectly heated recycle gas operated continuous dryers are right consuming. There are new attempts to reduce the burden of low-emission operation Wood chips dryers to lower. For this purpose, it is proposed according to WO 01/67016 A1, the total surplus the Umgasstromes a directly with flue gases heated Umgastrockners attributed to the firing and the resulting surplus thermally cleaned flue gases for the likewise direct heating to use pre-drying, also rubbed with circulating air, wherein in the pre-drying due to much lower temperatures through higher Moisture less decomposition products are formed.

When drying mechanically insensitive goods, or when working in a process with comminution anyway, very good material and heat transfer are achieved with spin dryers. Due to the very good separation of the dry material is almost the entire specific outer surface of the dry material at the same time high turbulence for the mass and heat exchange available. An interesting spin-dryers claims the EP 0 862 718 B1 , This pneumatic centrifugal dryer with stationary type, indirectly heated by Umgas, combines in one container an axially standing centrifugal shaft with a classifying flow dryer. Here granules of defined grain size are produced from a suspension. For the drying of wood fibers and similar botanicals, however, this pneumatic centrifugal dryer with Umgasbetrieb seems less suitable.

task The present invention is a method and an apparatus for the indirect drying of pneumatically conveyable goods, in particular wood fibers and similar herbal substances, with very good separation of the dry material and using the wall of the drying room as a heat exchanger, without the aforementioned To create disadvantages.

The solution This object is specified in claim 1 or 5.

In 1 the main elements of the invention are shown: The from induced draft 3 , Suction tube 4 and downpipe 5 existing loop reactor is in an oven 6 , The good 1 is given up wet and the spin dryer leaves bridal steam and dried material 2 ,

Of the Pneumatic centrifugal dryer according to the invention combines the very good heat transfer of the spin dryer with the very simple control behavior of the Loop reactor, which approximately that of the ideal stirred tank equivalent. As a stream dryer, it is especially suitable for drying hard-to-handle goods like wood fibers and the like herbal substances suitable. In contrast to today's common solutions indirectly heated stream dryer but eliminates the costly entry the heat of vaporization over a Brüdenkreislauf with different apparatus and those required for low overheating of the vapors extremely high gas circulation or for less upheaval required high vapor overheating with product decomposition. According to claim 5 is the spin dryer directly in an oven. The burned flue gas is due to the recirculation abruptly to oven temperature of e.g. Cooled to 450 ° C and overheated on the reactor wall vapors of e.g. 150 ° C Heat is immediately removed by the drying process. For 1 kg of water evaporation are used e.g. 10 kg of vapor circulated. The independent Residence times of the dry material and the vapors are usually the same 10 to 300 seconds.

The dry matter-vapor mixture is circulated in the loop reactor with a transport impeller, as it is known from the induced draft of the pneumatic chip conveyor. This is a very robust open radial fan with closed back, where nothing gets stuck. When passing through the transport wheel and when spinning against the reactor wall, the dry material is very well isolated, as in any spin dryer. The dry matter particles rubbing down the reactor wall in the downpipe cause a thin PRANDEL boundary layer and thus an excellent heat transfer from the wall to the wall circulated vapors.

at internal upheaval is the guide tube present in this case in a loop reactor designed as a suction tube, the induced draft is directly on the intake manifold and hurls the dry material against the blower as a heat exchanger functioning reactor wall. To enlarge the heat exchanger surface is It is advantageous to work with several downpipes that have one Distributor head fed absolutely evenly become.

Basically the spin dryer according to the invention also be operated by means of suction at the bottom, the transport wheel at the same time floor mixer can be. In this case, an external circulation of the dry material / vapor mixture takes place. This execution, in which the entire machine technology is mounted at ground level, can for smaller ones Dryer be very beneficial.

in the Interior of the pneumatic according to the invention Spin dryer will heat from the dryer wall without much overheating the vapors transported to the dry goods. Due to the thermal inertia of Dryer wall can in case of failure of the Loading with dry material very quickly a the entire drying room reaching emergency cooling with eingedüstem Water done. Thus, the special fire risk of the drying process vegetable Substances are practically excluded. If it nevertheless once to Brand should come, this will be by deporting all openings just smothered. Should an impermissible overpressure be built up, this will be over Pressure relief flaps dismantled.

Of the pneumatic centrifugal dryer can be very well according to the internal temperature of the loop reactor. The residual moisture correlates for a given product very well with this temperature. To start the dryer is preheated to operating temperature and then slowly wet material is added in such an amount that the internal temperature constantly remains in the target value range. The property task is steadily increased until the stove wall is fully heated and the full firing capacity for the Drying available is. To shut down the firing is set and as long as decreasing charge continues to be dried until safely switched off can be. The dryer can also spray water quickly by evaporating deflated and cooled become.

to Cogeneration can the pneumatic centrifugal dryer by means of exhaust gas of a gas turbine be heated or with exhaust steam of a steam engine, a back pressure turbine or a withdrawal condensing turbine. For steam heating, the Downpipes are also designed as double-jacket pipes. For steam an organic liquid For example, the pneumatic spin dryer can be used as the condenser of an ORC power plant become.

Especially suitable is the spin dryer according to the invention for the Decentralized processing of renewable resources. Have for this the plants preferably a firing capacity of 0.3 to 3 MW. High cost-effectiveness is achieved by increasing the price of biomass reached. Thus, e.g. in the production of wood fibers by means of Twin-screw extruder from LEHMANN MASCHINENBAU GMBH JOCKETA from wet wood chips from Ganzbaumernte the fines, which contains a high proportion of bark and needles or foliage, through Air views separated and burned directly in a Vorofenfeuerung become. The wind sifter can on the current fuel demand be set. In this case, there is only one common line for raw material and Fuel.

In the pneumatic centrifugal dryer according to the invention the dry material is separated very well as in every spin dryer, so that in usually almost the entire specific surface of the dry material for the fabric and heat exchange with the vapors to disposal stands and achieved by the high turbulence very good mass and heat transfer become. Up to the breakpoint moisture is the rate-limiting Step of heat input in the dryer. For Drying up to the break point moisture content is therefore the residence time behavior of the simple stirred tank sufficient. For Further drying, such as for chipboard bonding is required even two or more dryers are connected in series as a cascade, only for the diffusion-controlled final drying below the break point moisture higher temperatures to drive in the dryer. Also can in the main drying two or more spin dryers in parallel work and with a common spin dryer for final drying be connected in series.

The dry matter discharged from the spin dryer can be removed pneumatically with air. The sensible heat of the dry material is still used for subsequent drying by evaporative cooling. Even better is the efficiency when the transport air is previously heated with waste heat. The used transport air is advantageously used as combustion air in the furnace of the dryer. In the case of flammable dry material, such as vegetable materials, no further dedusting is required after the product separator. Although the water vapor from the after-drying must be heated with the flue gases to exhaust gas temperature, which requires but only a fraction of the saved heat of evaporation.

Of the pneumatic centrifugal dryer is preferably also pneumatic fed. If for Transport air is used, although the water vapor partial pressure drops in the dryer, what for The drying is advantageous, but also decreases the dew point temperature the vapors, what kind of the waste heat utilization is disadvantageous. flash steam should be overheated as a transport gas to avoid dew point violations. By such Brüdenüberhitzung with an exhaust gas cooler the efficiency is improved. The pneumatic spin dryer but can e.g. also with a screw conveyor be charged.

flash steam With high dew point temperature is known to be very good for the use of waste heat suitable. Often, however, the heat requirement is missing at the place of occurrence. Renewable raw materials intended for drying are often wet. In this case, it may be advantageous to use raw materials with vapor vapor to dampen, to save heating in the dryer. The expiring during steaming Water is usually very good to clean biologically. Such a damper causes at the same time a dedusting of the vapors.

Of the flash steam but can e.g. be condensed in an air cooler, the uncondensed portion is fed directly or indirectly to the furnace and the heated air can be used for pre- or post-drying become. So can chopped forage pre-dried in a pneumatic spin dryer and subsequently dried on a belt dryer become. The green fodder is aerated much better after pre-drying and the heating energy is used twice here. Or woodchips are used for making of fuel pellets in silos with soil aeration through this warm air pre-dried, crushed in a hammer mill, dried in a pneumatic spin dryer and then pelletized.

Example 1: Plant and Process for processing woodchips into wood fibers with drying in one embodiment the dryer according to the invention.

The most important dimensions are approximately: Eight downpipes 508 × 8 mm with 12,750 mm drop height. The suction tube 406.4 × 12 mm, the distribution head of square hollow section 150 × 10 mm and hemispherical collector 2,600 mm diameter, 1300 mm height and 10 mm wall thickness. This loop reactor is made of material St 37-2. The furnace wall has an inner diameter of 2,400 mm and an outer diameter of 3,000 mm and is stuffed with mineral insulating wool to about 100 kg / m ³ . The inside of the furnace wall consists of a 1 mm thick metal jacket made of material 1.4713, which is provided with cross beads for stiffening and length compensation. The combustion chamber for a wood injection firing and all thermally highly loaded kiln installations are made of material 1.4762. The entire heat exchanger surface is about 180 m ² . Depending on the material and wall temperature, the maximum evaporation capacity for water is approx. 1,200 to 2,400 kg / h. Thereafter, the firing capacity is designed depending on the specific circumstances to 0.99 to 2.7 MW, with basically any fuel is possible. The specific power consumption of the induced draft is 0.01 to 0.06 kWh / kg water evaporation. The loop reactor with oven wall is the largest item for assembly and, with a dimension of 3,000 × 3,000 × 16,000 mm, presents no problems for road transport.

The Wet chips are discharged from the bunker by means of a sliding floor to the air classifier, where the fine fraction depends on the respective heat requirement of the dryer discharged by means of transport air and in a Vorofenfeuerung blown.

The From the fines separated wood chips arrive via a conveyor belt in the damper, where the coarse-grained Heap is well flowed by Brüdendampf. The condensed vapors and the expired from the wood chips become a biological Cleaning supplied. Out of those in dampers dedusted vapors is depending on other heat demand waste heat in a condenser with 80 ° C Return temperature recovered.

The steamed be called Wood chips are a twin-screw extruder from LEHMANN MASCHINENBAU GMBH JOCKETA for defibration and arrive from there a screw conveyor in the suction tube of the dryer.

In the spin dryer, the wood fiber-vapor mixture is sucked at the lowest point of the collecting device from the suction pipe, wherein above the collecting device in the suction pipe and the fresh material is supplied. Above the suction tube is a transport wheel, as it is known from the chip conveyor, mounted with a vertical axis in the distributor head hanging. The distributor head corresponds to the housing of a radial blower with the difference that it has several arranged around a symmetry axis of rotation outlets, here eight pieces. The transport impeller hurls the aspirated wood fiber-vapor mixture through the outlets of the distributor head with tangential entry into the downpipes, where the wood fibers are thrown against the wall on a spiral path down and fall together with the circulated vapors get into the collection device, where they are sucked again.

At the Bottom of the collector ensures a Bodenrührwerk that no wood pulp settles and therefor, that constantly wood fibers be transported in the departure, from where they with the vapors to the Arrive cyclone.

The Einblasfeuerung is designed as a pre-furnace, so that the fine fraction the wet wood chips for a clean combustion is achieved necessary combustion chamber temperature becomes. The actual oven room of the spin dryer stands up the hemispherical one Collection device of the loop reactor and covers the entire remaining part of the Loop reactor, except for the drive of the transport wheel. The about 400 ° C be called Exhaust gases of the furnace are in the air preheater to about 200 ° C chimney temperature cooled.

Example 2: Method for the production of fuel pellets from wet sawdust.

From a controllable feed belt is the pneumatic centrifugal dryer via a rotary valve loaded with sawdust in a pneumatic Baypass. In a cyclone separator The dried sawdust are separated from the vapors and over a rotary valve directly a pellet press of the company MÜNCH, RATINGEN fed. The optimum degree of dryness of sawdust is determined by the appearance of the Pellets assessed and the speed of the feed belt increased accordingly or decreased. Due to the hot steam short-term drying deleted the otherwise required conditioning and the intermediate buffer.

Example 3: Method for self-sufficient sewage sludge drying with direct combustion and optional phosphate recovery.

The dry organic matter (oTS) of municipal sewage sludge has about the calorific value as dry wood. With filter presses or Centrifuges mechanically dehydrated sewage sludge with at least 20% oTS can therefore be burned autothermally. To the prior art, the sewage sludge is dried and the dry goods can for the heating of the dryer will be burned. As the sewage sludge When drying passes through a so-called glue phase, he must for drying in convection dryers by backmixing with dry material on over 60% TS can be set. By the internal product return is the inventive pneumatic Centrifugal dryer for this best for. In the collecting device a kneader is installed, which the mixing too crumbly Consistency causes.

Of the powdery dry sewage sludge is in a cyclone from the brothers steam roughly separated and preheated Air in an eddy current burner of the GIV MBH, HALLE very clean burned. The dusty vapors become directly the secondary combustion chamber supplied and thus thermally cleaned. With the completely burned out flue gases the steam generator is heated. The steam engine of the generator is operated with 16 bar back pressure and the dryer acts as Capacitor.

By mono-incineration can remove ash from sewage sludge without heavy metal pollution can be used directly as biocide-free phosphate fertilizer, otherwise is a further treatment for the phosphate recovery required.

Claims (10)

Method for drying pneumatically conveyed Goods in an indirectly heated spin dryer, in which the dry matter-vapor mixture is pneumatically circulated by means of transport wheel in such a way that the dry matter in the falling stream by centrifugal force against the as a heat exchanger acting reactor wall is spun. Method according to claim 1 with pneumatic supply of the Dry good for spin dryer, with Brüdendampf as a transport medium is used, which may optionally also be overheated, in particular in an exhaust gas cooler. The method of claim 1 with dissipation of the heat of condensation vapors, preferably with disposal of the non-condensable portion of the vapors on the Firing the spin dryer. The method of claim 1 with downstream pneumatic advancement for waste heat utilization by Evaporative cooling; wherein the transport air used preferably the firing of the spin dryer supplied becomes. Device for the method of claim 1 with a spin dryer directly in an oven, which with a furnace or with hot exhaust gases is heated. Device for The process of claim 1, wherein the process is indirect with steam is heated. Apparatus according to claim 5 or 6, wherein the spin dryer consists essentially of a vertical cylindrical container and a free-blowing suction draft with suction pipe, the induced draft being arranged so that by means of suction pipe above the bottom of the container dry material Brü The mixture can be sucked and can be thrown against the uppermost part of the wall of the cylindrical container by the free-flowing transport wheel of the induced draft dry material. Apparatus according to claim 5 or 6, wherein the spin dryer has several downpipes, the top above tangential inflow are connected to a distributor head, which via a transport line with connected to the collecting pipes arranged under the downpipes is. Apparatus according to claim 5 or 6 with one or several floor mixers to prevent deposits from drying on the bottom of the slingshot and optionally also in the lower part of the suction tube and optionally also with agitator blading for transportation from dry material to the suction pipe and / or to the outlet. Apparatus according to claim 5 or 6, wherein two or more spin dryer make a cascade.